Enya 4 cycles run very well on 5% to 10% nitro fuel. Enya recommends (at least in the instructions I have seen) a castor / synthetic blended fuel for the four strokes. Any of the castor/ syntetic blended airplane fuels on the market should serve you just fine. Remember that these engines are designed for lower nitro than some of the other 4-cycles out there, anything more than 15% is a waste and actually makes them run erratic. I usually use 10% in my Enya 4 cycles.